System and Method for Shape Memory Alloy Thermal Interface

ABSTRACT

An apparatus includes a thermally conductive interface assembly including a first component associated with a first interface surface and a second component associated with a second interface surface. The apparatus also includes a shape memory alloy component coupled to the thermally conductive interface assembly and configured to move one or more components of the thermally conductive interface assembly between a first state and a second state based on a temperature of the shape memory alloy component. In the first state, the first interface surface is in physical contact with the second interface surface, and in the second state, a gap is defined between the first interface surface and the second interface surface.

FIELD OF THE DISCLOSURE

The present disclosure is generally related to thermal interfaces usingshape memory alloys.

BACKGROUND

A thermal interface transfers heat between two objects, such as a heatsource and a heat sink. A thermal interface is often used to remove heatgenerated from an electronic device. A small temperature differencebetween a hot side and a cold side of the thermal interface (e.g., whenthe thermal interface is exposed to external or environmental loads,such as higher temperatures/solar radiation) causes the thermalinterface to become less effective at rejecting heat from the electronicdevice. In some operating conditions, the thermal interface is unable toremove a sufficient amount of heat from the electronic device oractually transfers heat from the external source or environment to theelectronic device, thus damaging the electronic device.

In the context of a spacecraft (e.g., a spaceship, a satellite, or aspace station), as the spacecraft operates (e.g., orbits an astronomicalbody) the spacecraft typically has one surface that experiencesrelatively high environmental loading and has another surface thatexperiences relatively low environmental loading. For example, thesurface of the spacecraft that faces the Sun experiences high solarradiation and temperatures as compared to the surface of the spacecraftfacing away from the Sun. The surface that faces the Sun may change overtime as the spacecraft operates. In some operating conditions, thesurface that faces the Sun cannot be used effectively to transfer orreject heat into space from the spacecraft and/or electronic devicesthereof.

Additionally, generally only surfaces that are protected from highlevels of solar radiation can be used as radiative surfaces. Thislimitation on which surfaces can be used means that some surfaces (e.g.,surfaces that face the Sun) cannot be used to reject heat.Alternatively, complicated protection schemes, such as a thermal shield(e.g., louvers or blinds) may be used to reflect solar radiation fromthe Sun and reduce the amount of solar radiation absorbed by theradiative surfaces and the thermal interface. Variable conductance heatpipes may be used throughout the spacecraft to transfer heat fromelectronic devices to a radiative surface that transfers (e.g., rejects)heat into space. Alternatively, a spacecraft may include heat pumps totransfer (or pump) the heat from the electronic device to the radiativesurface. These solutions to reject heat energy add complexity, weight,and volume to spacecraft design. In the context of a spacecraft, thesefactors greatly increase cost.

SUMMARY

In a particular implementation, an apparatus includes a thermallyconductive interface assembly including a first component associatedwith a first interface surface and a second component associated with asecond interface surface. The apparatus also includes a shape memoryalloy component coupled to the thermally conductive interface assemblyand configured to move one or more components of the thermallyconductive interface assembly between a first state and a second statebased on a temperature of the shape memory alloy component. In the firststate, the first interface surface is in direct physical contact withthe second interface surface, and in the second state, a gap is definedbetween the first interface surface and the second interface surface.

In another particular implementation, a spacecraft includes anelectronic device and one or more heat pipes coupled to the electronicdevice. The spacecraft also includes a thermally conductive interfaceassembly coupled to the one or more internal heat pipes. The thermallyconductive interface assembly includes a first component that has afirst interface surface and a second component that has a secondinterface surface. The spacecraft further includes a shape memory alloycomponent coupled to the thermally conductive interface assembly andconfigured to move one or more components of the thermally conductiveinterface assembly between a first state and a second state based on atemperature of the shape memory alloy component. In the first state, thefirst interface surface is in physical contact with the second interfacesurface, and in the second state, a gap is defined between the firstinterface surface and the second interface surface.

In another particular implementation, a method of transferring heat froma spacecraft includes moving, by a shape memory alloy component of athermally conductive interface assembly, one or more components of thethermally conductive interface assembly from a first state to a secondstate responsive to a first temperature. In the first state, a firstinterface surface of the thermally conductive interface assembly is inphysical contact with a second interface surface of the thermallyconductive interface assembly, and in the second state, a gap is definedbetween the first interface surface and the second interface surface.The method also includes moving, by the shape memory alloy component,the one or more components of the thermally conductive interfaceassembly from the second state to the first state responsive to a secondtemperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram that illustrates an example of a thermallyconductive interface assembly:

FIG. 2 is a diagram that illustrates an example of a thermallyconductive interface assembly that is activated by environmentalheating:

FIG. 3 is a diagram that illustrates another example of a thermallyconductive interface assembly that is activated by environmentalheating;

FIG. 4 is a diagram that illustrates an example of a thermallyconductive interface assembly that includes a heating element:

FIG. 5 is a diagram that illustrates another example of a thermallyconductive interface assembly that includes a heating element:

FIG. 6 is a diagram that illustrates an example of a thermallyconductive interface assembly that includes mechanical linkage;

FIG. 7 is a diagram that illustrates an example of a shape memory alloyframe of a thermal interface material;

FIG. 8 is a diagram that illustrates another example of a shape memoryalloy frame of a thermal interface material;

FIG. 9 is a flow chart of an example of a method for transferring heatusing a thermally conductive interface assembly; and

FIG. 10 is a block diagram that illustrates an example of a spacecraft.

DETAILED DESCRIPTION

Implementations disclosed herein are directed to a thermal interfaceassembly including shape memory alloy components and having a variableconductance thermal interface. For example, components of the thermalinterface assembly are movable to couple (e.g., mate) and decouple(e.g., separate) a conductive thermal interface of the thermal interfaceassembly using the shape memory alloy components. A thermal interfaceassembly having a variable conductance thermal interface can be used ina vehicle (e.g., a spacecraft) to control heat rejection from thevehicle and electronic devices thereof. The thermal interface assemblymay be coupled to a radiator (e.g., an exterior surface) to selectivelycontrol heat rejection. For example, the thermal interface assemblyenables heat transfer when the conductive thermal interface is coupledand impedes heat transfer when decoupled. The variable conductancethermal interface may enable any surface of the vehicle to be used forselective heat rejection without adding heavy and/or complicated thermalbarriers or control systems.

An exemplary thermal interface assembly includes a first component, asecond component, one or more fasteners, and a shape memory alloycomponent. A first surface of the first component, a thermal interfacematerial or materials, and a second surface of the second component forma thermal interface of the thermal interface assembly. The thermalinterface allows conductive heat transfer between the first component,the thermal interface material(s), and the second component when thethermal interface is closed (e.g., conductive heat path from the firstsurface to the second surface via the thermal interface) and preventsconductive heat transfer between the first component and the secondcomponent when the thermal interface is open (e.g., the surfaces are notin contact via the thermal interface material). In some implementations,a heat pipe is coupled to each of the first component and the secondcomponent to provide heat to and remove heat from the thermal interface.

For example, a first heat pipe removes heat from an electronic deviceinside the vehicle and transfers the heat to the thermal interfaceassembly via conduction and radiation (and possibly convection if afluid is present, such as air). A second heat pipe is coupled to aradiator (e.g., an exterior surface). When solar radiation input to theradiator is low (e.g., the radiator faces away from the Sun or iscoupled to a surface that faces away from the Sun), the second heat pipereceives heat (via conduction) across the thermal interface from thefirst heat pipe and transfers the heat to the radiator by conduction andradiation (and possibly convection if a fluid is present, such as air).When solar radiation input is high (e.g., the radiator faces the Sun oris coupled to a surface that faces the Sun) and the surfaces of thermalinterface assembly are not in contact, heat is absorbed by the radiatorand the second heat pipe, but the heat is not transferred across thethermal interface by conduction.

The shape memory alloy component rearranges its shape or configurationbased on temperature and exerts a relatively large force (compared toother metals during thermal expansion and contraction) duringrearrangement. The rearranged shape may be an expanded shape, acompressed shape, a twisted shape, an untwisted shape, etc. Therearranged shape of the shape memory alloy component can be utilized togenerate a force to bias or move the thermal interface assembly betweenstates. For example, a first state corresponds to an open state wherethe first surface and the second surface are not in contact, and asecond state corresponds to a closed state where the first surface andthe second surface are in contact (either directly or via a thermalinterface material). In the first state, the first surface and secondsurface are separated by an insulator (e.g., an air or a vacuum gap).The thermal interface assembly has different conductive heat transfercharacteristics (e.g., a lower heat transfer coefficient) in the firststate as compared to the second state (e.g. the closed state). However,some conductive heat transfer may still occur in the first state via thefasteners. In the second state (e.g., the closed state) the firstsurface and the second surface are in contact via a thermally conductivematerial (e.g., a thermal interface material) and exchange heat throughconduction via the thermally conductive material.

In some implementations, the shape memory alloy component experiences atemperature change based on the environment directly (e.g., by absorbingsolar radiation), indirectly (e.g., by receiving energy from the solarradiation through conduction), or both. In response to the shape memoryalloy component reaching a first temperature, the shape memory alloyexperiences a solid-state phase change and reconfigures to a “programmedstate”. In some implementations, the shape memory alloy componentreconfigures to a “second programmed state” in response to reaching asecond temperature. The shape memory alloy may exhibit hysteresis, thatis the solid-state transition between the programmed states may occur atdifferent temperatures depending on a current state. Accordingly, thefirst temperature may be different than the second temperature.

In other implementations, the shape memory alloy component is coupled toor includes a heating element that is configured to provide heat to theshape memory alloy component. The temperature of the shape memory alloycomponent can be controlled to control rejection of heat. For example,the heating element can heat the shape memory alloy component to thefirst temperature or to the second temperature to move (e.g., configure)the thermal interface assembly to the first state or to the secondstate.

Depending on the configuration of the thermal interface assembly and thehow the shape memory alloy is programmed (e.g., formed or trained), thethermal interface assembly can be configured such that the thermalinterface is open when the shape memory alloy component is hot or whenthe shape memory alloy component is cold. Said another way, the thermalinterface assembly may be configured such that the shape memory alloycomponent is configured to generate a force to bias the thermalinterface open or to bias the thermal interface closed. To illustrate,the shape memory alloy component can be configured (e.g., programmed ortrained) to expand or to compress at hot temperatures to generate aforce. The force generated by the shape memory alloy component is usedto bias the thermal interface assembly towards the first state or towardthe second state. As an illustrative example, an increase in temperaturecauses the shape memory alloy to expand and to exert a force to open thethermal interface or causes the shape memory alloy to contract orcompress and to exert force to close the thermal interface.

Generally, a shape memory alloy component exerts a larger force as theshape memory alloy component transitions from a lower temperature solidstate (martensite) into a higher temperature solid state (austenite) andexerts a smaller force as the shape memory alloy component cools fromthe higher temperature solid state (austenite) into the lowertemperature solid state (martensite). Additionally, during cooling andwhen in the lower temperature solid state (martensite), the shape memoryalloy component can be more readily deformed by external forces ascompared to during heating and when in the higher temperature solidstate (austenite). Even when a shape memory alloy component isprogrammed or trained to have a compressed shape (e.g., shorter beamlength, less thickness, or both as compared to an original shape orexpanded shape) when in the higher temperature solid state (austenite),the shape memory alloy component still generates greater forces whentransition to the higher temperature solid state (austenite) than whentransitioning to the lower temperature solid state (martensite).Accordingly, the shape memory alloy component generally generatesgreater forces during reconfiguration (or transformation) to aprogrammed or a trained shape (e.g., a shape associated with theaustenite state) than forces generated during reconfiguration to anunprogrammed or untrained shape (e.g., a shape associated with themartensite state). The difference in forces may be used to controlmovement of the thermal interface assembly when balanced againstexternal loads generated by other components, such as fasteners andsprings.

By using a thermal interface with shape memory alloy component orcomponents to control heat transfer, the vehicle is smaller, lighter,and has reduced costs as compared to systems that use thermal shields,variable conductance heat pipes, or heat pumps. In the context of aspacecraft, the spacecraft would have reduced materials costs andreduced launching costs. In addition, the spacecraft, or rockets thatlaunch the spacecraft into space have fixed payload weights and physicalsize requirements. Additionally, the thermal interface enables selectionor control of heat transfer properties and enables increased heattransfer efficiency. For example, more surfaces of the vehicle or alarger portion of the surface of the vehicle can be used to reject heat.

FIG. 1 is a diagram 100 that illustrates an example of a thermallyconductive interface assembly 102. In FIG. 1, the diagram 100 includes afirst representation of the thermally conductive interface assembly 102in a first state 180 and a second representation of the thermallyconductive interface assembly 102 in a second state 190. In someimplementations, the thermally conductive interface assembly 102 isincluded in a vehicle 101 (e.g., a spacecraft) and is coupled to anelectronic device 104 thereof, as shown in FIG. 1. The thermallyconductive interface assembly 102 may be included in a heat rejectionsystem of the vehicle 101 to control or regulate rejection of heat fromthe vehicle 101, from the electronic device 104, or both. In someimplementations, control of the thermally conductive interface assembly102 is passive, as described further with reference to FIGS. 2 and 3.Additionally, or alternatively, the thermally conductive interfaceassembly 102 (or a portion thereof) can be actively controlled, asdescribed further with reference to FIGS. 4 and 5.

The thermally conductive interface assembly 102 includes a firstcomponent 112 associated with a first interface surface 152 and a secondcomponent 114 associated with a second interface surface 154 thatopposes the first interface surface 152. The first interface surface 152and the second interface surface 154 define a gap 160 depending on astate of the thermally conductive interface assembly 102. For example,the first interface surface 152 and the second interface surface 154define the gap 160 in the first state 180 and are in contact in thesecond state 190 (e.g., the thermally conductive interface assembly 102does not include the gap 160 in the second state 190). The firstinterface surface 152 and the second interface surface 154 are incontact when the first interface surface 152 is in conductive contactwith the second interface surface 154, such as directly or via one ormore thermal materials or layers of conductive materials. The firstinterface surface 152 and the second interface surface 154 are not inconductive contact when an insulator (e.g., the gap 160) separates thefirst interface surface 152 and the second interface surface 154. Thegap 160 may include air or, such as when in space, nothing (e.g., avacuum). In some implementations, the thermally conductive interfaceassembly 102 includes a third state having a smaller gap than the gap160.

In some implementations, such as illustrated in FIG. 1, the firstinterface surface 152 corresponds to a first surface of the firstcomponent 112 and the second interface surface 154 corresponds to asurface of a thermal interface material 136 associated with (e.g.,coupled to) the second component 114. The thermal interface material 136may be coupled to the first interface surface 152, the second surface ofthe second component 114, or both. As illustrated in FIG. 1, the thermalinterface material 136 is coupled to the second surface of the secondcomponent 114. The thermal interface material 136 includes orcorresponds to a solid material (e.g., a gasket or a thermal pad) or agel material (e.g., a thermal compound or paste). The thermal interfacematerial 136 is configured to increase thermal contact and thermalconduction between the first interface surface 152 and the secondinterface surface 154. For example, the thermal interface material 136fills in gaps between the first interface surface 152 and the secondinterface surface 154 that would otherwise be filled with air (or in thecontext of space, nothing). In some implementations, the thermalinterface material 136 includes a shape memory alloy component, asdescribed further with to FIGS. 7 and 8. In other implementations, thefirst interface surface 152, both of the interface surfaces 152 and 154,or neither of the interface surfaces 152 and 154 correspond to a surfaceof a thermal interface material. In a particular implementation, thefirst component 112 includes the first interface surface 152 and thesecond component 114 includes the second interface surface 154.

The thermally conductive interface assembly 102 includes one or morefasteners, such as fasteners 122-132. The fasteners 122-132 areconfigured to couple together components of the thermally conductiveinterface assembly 102 and to move one or more component of thethermally conductive interface assembly 102. For example, a first subsetof fasteners may be configured such that the first subset fastenersexert a force to bias the thermally conductive interface assembly 102towards the first state 180 and a second subset of fasteners may exert aforce to bias the thermally conductive interface assembly 102 towardsthe second state 190. The fasteners 122-132 include or correspond tobolts, screws, rivets, staples, pins, nails, nuts, washers, caps,springs, Belleview washers, etc.

The thermally conductive interface assembly 102 includes at least oneshape memory alloy component. For example, one or more fasteners of thefasteners 122-132, the thermal interface material 136, or a combinationthereof, include or correspond to a shape memory alloy component. Asillustrated in FIG. 1, the fasteners 130 and 132 are shape memory alloycomponents (also referred to as shape memory alloy components 130 and132). In another particular implementation, the shape memory alloycomponent includes or corresponds to a camshaft that is configured torotate a cam. Rotation of the cam generates a force to bias thethermally conductive interface assembly 102 towards the second state190, as further described with reference to FIG. 6.

The shape memory alloy component is configured to change (e.g.,reconfigure) to a programmed shape based on temperature and to undergo arelatively large displacement and exert a large force (compared to othermetals during expansion and contraction). The programmed shape maycorrespond to an expanded shape, a compressed shape, a bent shape, aflattened shape, a twisted shape, or an untwisted shape, relative to anoriginal shape. The programmed shape of the shape memory alloy isutilized to vary a conductive thermal interface of the thermallyconductive interface assembly 102. As compared to non-shape memorymetals or alloys, shape memory alloys are capable of being programmed ortrained for either compression or expansion (e.g., extension) upon anincrease in temperature. By using a shape memory alloy component that isprogrammed or trained to compress upon heating, the two interfacesurfaces 152 and 154 can be reconfigured from the first state 180 withthe gap 160 to the second state 190 (e.g., a thermally conductive state)by heating the shape memory alloy components which undergo a compressiveshape change, as described further with reference to FIGS. 2 and 5.Additionally or alternatively, the shape memory alloy components can beprogrammed or trained to expand when heated to open the thermalinterface (e.g., separate the first interface surface 152 from thesecond interface surface 154 and thermal interface material 136), asdescribed further with reference to FIGS. 3, 4, 7, and 8. Additionally,shape memory alloy components experience relatively large changes inshape and exert relatively large forces in response to temperaturechanges as compared to non-shape memory metal alloy components. Forexample, the martensite to austenite phase change that corresponds to atransition from a lower temperature to a higher temperature can generatedimension changes as large as 8% in the tensile or shear modes.Additionally, relatively small temperature changes may cause a shapememory alloy component to experience relatively large changes in shapeas compared to non-shape memory metal alloy components.

The shape memory alloy component changing shape may generate anadditional force which biases the thermally conductive interfaceassembly 102 towards a particular state (e.g., the first state 180) ormay increase an existing force which biases thermally conductiveinterface assembly 102 towards the particular state. Additionally oralternatively, the shape memory alloy component changing shape mayreduce an existing force (or cause a reduction in an existing force)which biases thermally conductive interface assembly 102 towards theother state (e.g., the second state 190). The additional force orreduction to the existing force changes a balance of forces of thethermally conductive interface assembly 102 such that the thermallyconductive interface assembly 102 switches from the particular state tothe other state.

In some implementations, the shape memory alloy component includes orcorresponds to a one-way memory shape memory alloy. A one-way memoryshape memory alloy has one programmed shape response to receiving heat.In other implementations, the shape memory alloy component correspondsto a two-way memory shape memory alloy. A two-way memory shape memoryalloy has two programmed shapes, a first programmed shape responsive toa first temperature (e.g., a higher temperature) and a second programmedshape responsive to a second temperature (e.g., a lower temperature).The shape memory alloy component may include alloys of two or moremetals, such as aluminum, copper, gold, hafnium, indium, iron, lead,nickel, magnesium, silver, titanium, zinc, etc. As illustrative,non-limiting examples, the shape memory alloy component includes anickel and titanium alloy (e.g., nitinol) or a copper and aluminumalloy.

In another particular implementation, the shape memory alloy componentis a sub-component of the fasteners 122-132 or the thermal interfacematerial 136. In such implementations, the shape memory alloy componentincludes or corresponds to tubing, threads, caps, pins, posts, ornotches of shape memory alloy material that are combined with or coupledto a particular fastener of the fasteners 122-132 or the thermalinterface material 136. For example, in a particular implementation thefastener 126 includes a steel screw with a steel head at a first end(e.g., a proximal end), a steel shank and/or threads, and a shape memoryalloy cap or pins at a second end (e.g., a distal end). Thus, as theshape memory alloy cap or pins at the second end reconfigure (e.g.expand) and exert a force against the first component 112, the firstinterface surface 152 and the second interface surface 154 separate toform the gap 160.

The thermally conductive interface assembly 102 may further include oneor more heat pipes, such as a first heat pipe 142 and a second heat pipe144 configured to exchange heat via the thermal interface. Asillustrated in FIG. 1, the first heat pipe 142 (e.g., an internal heatpipe) is coupled to the first component 112 and the second heat pipe 144(e.g., an external heat pipe) is coupled to the second component 114.

In some implementations, the thermally conductive interface assembly 102is coupled to a heat source, such as the electronic device 104. In theexemplary implementation illustrated in FIG. 1, the electronic device104 is coupled to the first heat pipe 142 of the thermally conductiveinterface assembly 102. In other implementations, the electronic device104 is coupled to the first component 112 directly or via anotherthermal interface.

In some implementations, the thermally conductive interface assembly 102is coupled to a radiator 106 (e.g., a radiative surface) configured toreject or dissipate heat by radiation (and possibly convection) to anenvironment. In a particular implementation, the radiator 106 is coupledto the second heat pipe 144 and corresponds to an exterior surface ofthe vehicle 101. In other implementations, the second component 114and/or the second heat pipe 144 may function as the radiator 106.

During operation of the vehicle 101, the electronic device 104 operatesand generates heat. Additionally, during the operation of the vehicle101, an exterior surface of the vehicle 101 that is coupled to thesecond heat pipe 144 may face the Sun and be externally loaded at afirst time by solar radiation and may face away from the Sun and not beexternally loaded by solar radiation at a second time. At the firsttime, the shape memory alloy components 130 and 132 of the thermallyconductive interface assembly 102 reach the first temperature responsiveto receiving (directly or indirectly) thermal energy from the Sun.Responsive to the first temperature, the shape memory alloy components130 and 132 experience a solid-state phase change (e.g., martensite toaustenite) and generate or cause a force to bias the thermallyconductive interface assembly 102 towards the first state 180 (open thethermal interface or create the gap 160 as illustrated in FIG. 1). Forexample, the force generated by the shape memory alloy components 130and 132 causes the shape memory alloy components 130 and 132 totransform to the compressed shape which reduces a force, generated byone or more of the fasteners 122-132, that biases the thermallyconductive interface assembly 102 towards the second state 190 (Thereduced force biasing the thermally conductive interface assembly 102towards the second state 190 is overcome by a force that is generated byone or more other components (e.g., the fasteners 126 and 128, a spacer,a spring, etc.) and that biases the thermally conductive interfaceassembly 102 towards the first state 180, resulting in the thermallyconductive interface assembly 102 having the first state 180.Additionally or alternatively, the compressed shape (e.g., a reducedvolume of the compressed shape) allows the force generated by the one ormore other components to bias the thermally conductive interfaceassembly 102 towards the first state 180. For example, the reducedvolume of the compressed shape shifts a static equilibrium point of thethermally conductive interface assembly 102 from being associated withthe second state 190 to being associated with the first state 180.

In the implementation illustrated in FIG. 1, a first fastener 122 and asecond fastener 124 correspond to bolts, a third fastener 126 and afourth fastener 128 correspond to screws, and a fifth fastener 130 and asixth fastener 132 correspond to nuts or washers. The fasteners 122-128exert a force that biases the thermally conductive interface assembly102 towards the second state 190. The fasteners 130 and 132 selectivelyexert a force that biases the thermally conductive interface assembly102 towards the first state 180 based on temperature. In theimplementation illustrated in FIG. 1, the fifth fastener 130 and thesixth fastener 132 have a compressed shape responsive to firsttemperature.

In the first state 180, the heat generated by the electronic device 104and heat within the vehicle 101 is not conductively transferred from thefirst heat pipe 142 to the second heat pipe 144 via the thermalinterface (i.e., contact between the first interface surface 152, thethermal interface material 136, and the second interface surface 154). Aportion of the heat generated by the electronic device 104 and a portionof the heat within the vehicle 101 is still conductively transferred viathe second component 114, the fasteners 122-128, and the first component112. Additionally, heat (e.g., solar radiation) from the radiator 106 isnot conductively transferred from the second heat pipe 144 to the firstheat pipe 142 via the thermal interface in the first state 180. Ascompared to the second state 190, less heat from the radiator 106 isconductively transferred from the second heat pipe 144 to the first heatpipe 142 via the second component 114, the fasteners 122-128, and thefirst component 112. Thus, thermally conductive interface assembly 102blocks or prevents absorption of a portion of solar radiation in thefirst state 180.

While in the first state 180, the heat generated by the electronicdevice 104 and the heat within the vehicle 101 may be rejected viaanother radiator (not shown) of the vehicle 101. In someimplementations, the other radiator (e.g., an exterior surface that isfacing away from the Sun) is coupled to another thermally conductiveinterface assembly of the vehicle 101. In a particular implementation,the other thermally conductive interface assembly is in the second state190 at the first time and while the thermally conductive interfaceassembly 102 is in the first state 180.

At the second time, the shape memory alloy components 130 and 132 of thethermally conductive interface assembly 102 reaches the secondtemperature responsive to receiving (directly or indirectly) relativelyless thermal energy from the Sun. Responsive to reaching the secondtemperature, the shape memory alloy components 130 and 132 experience asolid-state phase change (e.g., austenite to martensite) and cease togenerate or cause the force to bias the thermally conductive interfaceassembly 102 towards the first state 180 (open the thermal interface orcreate the gap 160 as illustrated in FIG. 1). Responsive to the shapememory alloy components 130 and 132 ceasing to generate or cause theforce to bias the thermally conductive interface assembly 102 towardsthe first state 180, the force generated by the one or more of thefasteners 122-132 biases the thermally conductive interface assembly 102towards the second state 190 (close the thermal interface and eliminatethe gap 160).

In the second state 190, the heat generated by the electronic device 104can be conductively transferred from the first heat pipe 142 to thesecond heat pipe 144 via the thermal interface (i.e., by physical orthermal contact between the first interface surface 152 and the secondinterface surface 154). Additionally, the heat generated by theelectronic device 104 can be transferred from the second heat pipe 144to the radiator 106 where the heat can be rejected. The radiator 106 mayinclude or correspond to an exterior surface of the vehicle 101. In suchimplementations, the thermally conductive interface assembly 102 may beincluded in a close-out panel of the vehicle 101. In the first state180, the thermal interface assembly has different conductive heattransfer characteristics (e.g., a lower heat transfer coefficient) ascompared to the second state 190.

In other implementations, a shape memory alloy component of thethermally conductive interface assembly 102 reconfigures to generate aforce to bias the thermally conductive interface assembly 102 towardsthe second state 190 (close the thermal interface and eliminate the gap160). In such implementations, the shape memory alloy componentreconfigures to an expanded shape, a compressed shape, a twisted shape,or an untwisted shape. Additionally, the thermally conductive interfaceassembly 102 may include other components, such a heating element, acontroller, one or more fastener connectors (e.g., heat spreaders), asdescribed further herein.

Therefore, a thermally conductive interface assembly can be designedsuch that the thermally conductive interface assembly is configured toselectively transfer heat from a vehicle or an electronic device thereofbased on an amount of solar radiation received by the thermallyconductive interface assembly. Accordingly, a vehicle can use anyexterior surface as a radiator and the thermally conductive interfaceassembly can self-regulate when to reject heat and when to stoprejecting heat (or reduce heat transfer into the vehicle). The thermallyconductive interface assembly has reduced costs as compared to existingimplementations because the thermally conductive interface assembly islighter and takes up less space than existing implementations. As thethermally conductive interface assembly is less complex (e.g., does notrequire an electric motor to drive louvers or blinds) the thermallyconductive interface assembly is more reliable.

FIGS. 2 and 3 illustrate examples of a passively controlled (e.g.,environmentally controlled or activated) thermally conductive interfaceassembly. Referring to FIG. 2, a diagram 200 depicts an example of afirst representation of the thermally conductive interface assembly 102in the first state 180 and a second representation of the thermallyconductive interface assembly 102 in the second state 190. In theimplementation illustrated in FIG. 2, each of the first fastener 122 andthe second fastener 124 correspond to a bolt, each of the fifth fastener130 and the sixth fastener 132 correspond to a shape memory alloywasher, and each of the third fastener 126 and the fourth fastener 128correspond to a nut.

The thermally conductive interface assembly 102 further includes aspacer 264 coupled to the first interface surface 152 or the secondinterface surface 154. The spacer 264 is configured to exert a force tobias the thermally conductive interface assembly 102 towards the firststate 180. In other implementations, the spacer 264 is configured toexert a force to bias the thermally conductive interface assembly 102towards the second state 190, as described with reference to FIG. 3. Insome implementations, the spacer 264 includes or corresponds to aspring. In the particular implementation illustrated in FIG. 2, thespacer 264 corresponds to a Belleview washer (e.g., a conical or diskspring) coupled to the second interface surface 150.

In some implementations, the thermally conductive interface assembly 102includes one or more fastener connectors 262 (e.g., heat spreaders)configured to absorb heat (e.g., solar radiation) and transfer the heatto one or more of the fasteners 122-132. In the implementationillustrated in FIG. 2, the fastener connector 262 is coupled to (e.g.,in contact with) the fifth fastener 130 and the sixth fastener 132 andenables heat transfer between the fastener connector 262, the fifthfastener 130, and the sixth fastener 132. The fastener connector 262includes a thermally conductive material. In a particularimplementation, the fastener connector 262 (or a portion thereof)includes a coating or finish configured to increase absorption of solarradiation. In the implementation illustrated in FIG. 2, the thermallyconductive interface assembly 102 may be included in a close-out panel266 of a spacecraft. In this implementation, the first component 112corresponds to an interior side of the spacecraft and the secondcomponent 114 corresponds to an exterior side (e.g., space) of thespacecraft.

A first fastener group 220 of the thermally conductive interfaceassembly 102 includes the first fastener 122, the third fastener 126,and the fifth fastener 130. The first fastener group 220 is configuredto exert a force on the first component 112 and the second component 114to bias the thermally conductive interface assembly 102 towards thesecond state 190.

In addition, the diagram 200 of FIG. 2 includes a first representationof the first fastener group 220 in the first state 180 and a secondrepresentation of the first fastener group 220 in the second state 190.As illustrated in FIG. 2, the fifth fastener 130 includes a shape memoryalloy washer that has a first size 272 (e.g., a vertical dimension asillustrated in FIG. 2) at the first temperature and has a second size274 at the second temperature. The first size 272 corresponds to thefirst state 180 of the thermally conductive interface assembly 102. Asillustrated in FIG. 2, the first size 272 is smaller than the secondsize 274. In FIG. 2, the first size 272 corresponds to the compressedshape, and the second size 274 corresponds to an original or expandedshape.

During operation of the spacecraft, the spacecraft includes an exteriorsurface (e.g., the close-out panel 266) coupled to the second heat pipe144 and coupled to one or more fasteners that face the Sun and that areexternally loaded at a first time by solar radiation. At the first time,the shape memory alloy components 130 and 132 of the thermallyconductive interface assembly 102 reaches the first temperatureresponsive to receiving (directly or indirectly) thermal energy from theSun. Responsive to the first temperature, the shape memory alloycomponents 130 and 132 experience a solid-state phase change andreconfigure to a compressed shape (e.g., the first size 272).Reconfiguring to the compressed shape generates a force to bias thethermally conductive interface assembly 102 towards the first state 180(open the thermal interface or create the gap 160 as illustrated in FIG.1). The force generated by the shape memory alloy components 130 and 132reduces a force generated by one or more of the fasteners 122-132 thatbiases the thermally conductive interface assembly 102 towards thesecond state 190. The reduced force biasing the thermally conductiveinterface assembly 102 towards the second state 190 is overcome by theforce generated by the spacer 264 that biases the thermally conductiveinterface assembly 102 towards the first state 180. Additionally oralternatively, the compressed shape (e.g., a reduced force or reducedvolume of the compressed shape) allows the force generated by the spacer264 to bias the thermally conductive interface assembly 102 towards thefirst state 180.

In the first state 180, the heat within the spacecraft is not to beconductively transferred from the first heat pipe 142 to the second heatpipe 144 via the thermal interface (i.e., not conductively transferredby contact between the first interface surface 152, the thermalinterface material 136, and the second interface surface 154).Additionally, heat (e.g., solar radiation) from the close-out panel 266and exterior fasteners (e.g., the fasteners 126-132) is not conductivelytransferred from the second heat pipe 144 to the first heat pipe 142 viathe thermal interface in the first state 180. The heat within thespacecraft may be rejected via another exterior surface (e.g., close-outpanel 266), such as an exterior surface that is facing away from the Sunand is coupled to another thermally conductive interface assembly.

At a second time, the second heat pipe 144 and the one or more fastenerscoupled to the exterior surface (e.g., the close-out panel 266) of thespacecraft face away from the Sun and are not externally loaded by solarradiation. At the second time, the shape memory alloy components 130 and132 of the thermally conductive interface assembly 102 reaches thesecond temperature responsive to receiving (directly or indirectly)relatively less thermal energy from the Sun. Responsive to reaching thesecond temperature, the shape memory alloy components 130 and 132experience a solid-state phase change and cease to generate the force tobias the thermally conductive interface assembly 102 towards the firststate 180 (open the thermal interface or create the gap 160 asillustrated in FIG. 1). Responsive to the shape memory alloy components130 and 132 ceasing to generate the force to bias the thermallyconductive interface assembly 102 towards the first state 180, the forcegenerated by the one or more of the fasteners 122-132 biases thethermally conductive interface assembly 102 towards the second state 190(close the thermal interface and eliminate the gap 160). The forcegenerated by the one or more of the fasteners 122-132 overcomes theforce generated by the spacer 264. The first fastener group 220 stillgenerates a net force to bias the thermally conductive interfaceassembly 102 towards the second state 190. In the second state 190, theheat within the spacecraft can be conductively transferred from thefirst heat pipe 142 to the second heat pipe 144 via the thermalinterface (i.e., contact between the first interface surface 152 and thesecond interface surface 154). Additionally, the heat within thespacecraft can be transferred from the second heat pipe 144 to theclose-out panel 266 and the exterior fasteners where the heat can berejected.

In other implementations, a shape memory alloy component of thethermally conductive interface assembly 102 reconfigures to generate aforce to bias the thermally conductive interface assembly 102 towardsthe second state 190 (close the thermal interface and eliminate the gap160). In such implementations, the shape memory alloy componentreconfigures to an expanded state, a twisted state, or an untwistedstate.

Referring to FIG. 3, an example of a diagram 300 that includes a firstrepresentation of the thermally conductive interface assembly 102 in thefirst state 180 and a second representation of the thermally conductiveinterface assembly 102 in the second state 190 is illustrated.

In the implementation illustrated in FIG. 3, each of the first fastener122 and the second fastener 124 corresponds to a shape memory alloyscrew and each of the third fastener 126 and the fourth fastener 128corresponds to a screw. The thermally conductive interface assembly 102of FIG. 3 further includes one or more spacers coupled to one or morefasteners of the fasteners 122-128. The one or more spacers areconfigured to generate a force to bias the thermally conductiveinterface assembly 102 towards the second state 190. In the particularimplementation illustrated in FIG. 3, the spacer 264 is coupled betweenthe third fastener 126 and the first component 112 and a second spacer364 is coupled between the fourth fastener 128 and the first component112. The spacer 264 and the third fastener 126 and the second spacer 364and the fourth fastener 128 exert forces to bias the thermallyconductive interface assembly 102 towards the second state 190.

The operation of FIG. 3 is similar to FIG. 2. In FIG. 3, the first andsecond fasteners 122 and 124 include shape memory alloy material andgenerate the force to bias the thermally conductive interface assembly102 towards the first state 180. In the particular implementationillustrated in FIG. 3, the first and second fasteners 122 and 124correspond to shape memory alloy screws. The first and second fasteners122 and 124 reconfigure to an expanded shape or an untwisted shaperesponsive to reaching the first temperature. Threads of the first andsecond fasteners 122 and 124 may be threaded with or into firstcomponent 112 or the second component 114. Depending on whether thethreads are threaded with or into the first component 112 or the secondcomponent 114, the fastener will move an opposite component relative toa threaded component. For example, the first fastener 122 will move thefirst component 112 relative to the second component 114 when the firstfastener 122 is threaded with the second component 114. Threads of thethird and fourth fasteners 126 and 128 may be threaded with or intofirst component 112 or the second component 114 and with or into acomponent opposite the component that the first and second fasteners 122and 124 are threaded with or into. For example, in the implementationillustrated in FIG. 3, the first and second fasteners 122 and 124 arethreaded with the second component 114 and the third and fourthfasteners 126 and 128 are threaded with the first component 112.

Alternatively, the passively thermally conductive interface assembliesof FIG. 2 or FIG. 3 may be designed such that higher environmentalloading closes the thermal interface. Such designs enable a system toutilize a thermally conductive interface assembly to reconfigure toreject heat or prevent absorption based on external or environmentalconditions. For example, a passively cooled aircraft or building mayreduce an amount of heat absorbed by a particular surface until suchconditions exist where heat can be rejected from particular surface. Toillustrate, a thermally conductive interface assembly of the aircraft orbuilding may be designed such that the particular surface absorbs lessheat when a temperature of the aircraft or building is at or below 72degrees and enables rejection of heat when the temperature of theaircraft or building is above 72 degrees.

By using environmental activation, a thermally conductive interfaceassembly may have reduced costs, increased durability (e.g., no movingparts or electronics), and have smaller volume and weight, as comparedto other thermal solutions and thermally conductive interface assembliesthat include heating elements.

FIGS. 4 and 5 illustrate examples of a thermally conductive interfaceassembly that includes a heating element. FIG. 4 illustrates aparticular design of a thermally conductive interface assembly whereactive heating is configured to bias the thermal interface towards thefirst state 180 to the gap 160. FIG. 5 illustrates a particular designof a thermally conductive interface assembly where active heating isconfigured to bias the thermally conductive interface assembly towardsthe second state 190 and to close the gap 160.

Referring to FIG. 4, an example of a diagram 400 that includes a firstrepresentation of the thermally conductive interface assembly 102 in thefirst state 180 and a second representation of the thermally conductiveinterface assembly 102 in the second state 190 is illustrated. In theimplementation illustrated in FIG. 4, each of the first fastener 122 andthe second fastener 124 corresponds to a shape memory alloy screw andeach of the third fastener 126 and the fourth fastener 128 correspondsto a screw. Threads of the first and second fasteners 122 and 124 may bethreaded with or into the first component 112 or the second component114. Threads of the third and fourth fasteners 126 and 128 may bethreaded with or into the first component 112 or the second component114. Additionally the threads of the third and fourth fasteners 126 and128 may be threaded with or into a particular component opposite anothercomponent that the first and second fasteners 122 and 124 are threadedwith or into. For example, in the implementation illustrated in FIG. 4,the first and second fasteners 122 and 124 are threaded with the firstcomponent 112 and the third and fourth fasteners 126 and 128 arethreaded with the second component 114.

The thermally conductive interface assembly 102 includes one or moreheating elements configured to generate heat and provide the heat to oneor more shape memory alloy components of the thermally conductiveinterface assembly 102. Each heating element of the one or more heatingelements is coupled to one or more fasteners of the thermally conductiveinterface assembly 102. In the implementation illustrated in FIG. 4, thethermally conductive interface assembly 102 includes a first heatingelement 482 coupled to the first fastener 122 and a second heatingelement 484 coupled to the second fastener 124. In otherimplementations, a particular heating element is coupled to or integralwith one or more shape memory components indirectly. For example, aheating element may be coupled to a fastener connector, such as thefastener connector 262 of FIG. 2. In a particular implementation, theone or more heating elements include or correspond to a resistive typeheating element.

The thermally conductive interface assembly 102 further includes acontroller 408 coupled (e.g., communicatively coupled) to the one ormore heating elements and configured to control operations of the one ormore heating elements. The controller 408 includes a processor andmemory storing instructions executable by the processor. The controller408 is configured to send control signals to the one or more heatingelements (or a power supply thereof). The controls signal may activatethe one or more heating elements or may cause a modification of avoltage or a current received by the one or more heating elements.Alternatively, the controller 408 includes the power supply and thecontroller 408 is configured to supply a power signal to the one or moreheating elements and to adjust the power signal.

During operation, the controller 408 activates (or adjusts an amount ofheat generated by) the heating elements 482 and 484 responsive to amanual input, a sensor input, or a combination thereof. For example, thecontroller 408 may activate the heating elements 482 and 484 responsiveto a user input. As other examples, the controller 408 may activate theheating elements 482 and 484 responsive to input from a temperaturesensor, a positioning sensor, or a timer. The activation of the heatingelements 482 and 484 may correspond to the second time (e.g., a radiatorcoupled to the thermally conductive interface assembly 102 experienceslow environmental loading), as described with reference to FIG. 1.

The heating elements 482 and 484 generate heat and cause the firstfastener 122 and the second fastener 124 to reach a first temperature492. Responsive to reaching the first temperature 492, the firstfastener 122 and the second fastener 124 reconfigure (or transform) intoa compressed shape or a twisted shape. For example, a length or volumeof the fasteners 122 and 124 may decrease and/or the fasteners 122 and124 may twist causing threads of the fastener 122 and 124 to bias thethermally conductive interface assembly 102 towards the second state 190(e.g., pull the components together). For example, the first fastener122 includes threads that are threaded into or with threads of thesecond component 114 to generate the force to pull the first component112 and the second component 114 together.

At a time (e.g., when a radiator coupled to the thermally conductiveinterface assembly 102 experiences high environmental loading)subsequent to activation of the heating elements 482 and 484, thecontroller 408 deactivates or adjusts the heat generated by the heatingelements 482 and 484 responsive to a manual input, a sensor input, or acombination thereof. The heating elements 482 and 484 cease generatingheat (or generate less heat) and cause the first fastener 122 and thesecond fastener 124 to reach a second temperature 494. Responsive toreaching the second temperature 494, the first fastener 122 and thesecond fastener 124 reconfigure (or transform) into an original shape,an expanded shape, or an untwisted shape. For example, a length orvolume of the fasteners 122 and 124 may increase and/or the fasteners122 and 124 may untwist causing threads of the fastener to bias thethermally conductive interface assembly 102 towards the first state 180(e.g., push the components apart). To illustrate, the threads of thefirst fastener 122 generate a force to push the first component 112 andthe second component 114 apart.

In other implementations, the thermally conductive interface assembly102 includes shape memory alloy bolts, washers, or nuts in addition, orin the alternative to the shape memory alloy screws (e.g., the first andsecond fasteners 122 and 124). In such implementations, the shape memoryalloy bolts, washers, or nuts are configured to have an expanded oruntwisted shape responsive to the first temperature 492. The expanded oruntwisted shape generates a force to bias the thermally conductiveinterface assembly 102 towards the first state 180.

Referring to FIG. 5, an example of a diagram 500 that includes a firstrepresentation of the thermally conductive interface assembly 102 in thefirst state 180 and a second representation of the thermally conductiveinterface assembly 102 in the second state 190 is illustrated. In theimplementation illustrated in FIG. 5, each of the first fastener 122 andthe second fastener 124 corresponds to a shape memory alloy screw.Threads of the first and second fasteners 122 and 124 may be threadedwith or into the first component 112 or the second component 114. Forexample, in the implementation illustrated in FIG. 5, the first andsecond fasteners 122 and 124 are threaded with the second component 114.

The thermally conductive interface assembly 102 includes one or moreheating elements, such as the first heating element 482 and the secondheating element 484, as described with reference to FIG. 4. Thethermally conductive interface assembly 102 further includes one or morespacers, such as the spacer 264, as described with reference to FIG. 2

The operation of the implementation illustrated in FIG. 5 is the reverseof the operation illustrated in FIG. 4. Thus, heating a shape memoryalloy component of the thermally conductive interface assembly 102generates a force to bias the thermally conductive interface assembly102 towards the second state 190. In FIG. 5, the first and secondfasteners 122 and 124 include shape memory alloy material and generatethe force to bias the thermally conductive interface assembly 102towards the second state 190. In the particular implementationillustrated in FIG. 5, the first and second fasteners 122 and 124correspond to shape memory alloy screws. The first and second fasteners122 and 124 reconfigure to a compressed shape or a twisted shaperesponsive to reaching the first temperature 492. The heat provided bythe heating elements 482 and 484 causes the first and second fasteners122 and 124 to reach the first temperature 492. The first and secondfasteners 122 and 124 reconfigure to an original shape, an expandedshape or an untwisted shape responsive to reaching the secondtemperature 494 and cease generating the force to bias the bias thethermally conductive interface assembly 102 towards the second state190.

In addition, the thermally conductive interface assembly 102 of FIGS. 4and 5 may include feedback control. For example, the controller 408 mayreceive data from a sensor and adjust the heat generated by one or moreheating elements. To illustrate, the controller 408 may receivetemperature data, interface separation data, or both, and determine toadjust the heat generated by one or more heating elements (e.g., thefirst heating element 482, the second heating element 484, or both). Insuch implementations, the thermally conductive interface assembly 102may include more than two states, such as third state where a second gapis smaller or larger than the gap 160.

By using heating element to control the thermally conductive interfaceassembly manual control and more precise control over heat rejectionfrom a vehicle is possible as compared to passive systems. Additionally,the thermally conductive interface assembly can use a shape memory alloycomponent to generate a force to bias the thermally conductive interfaceassembly towards the second state 190 (e.g., closed). Further, usingheating elements to control the thermally conductive interface assemblymay require less precision in the design process and enable the vehicleto operate in a wider range of temperatures and environments.

FIG. 6 is diagram 600 that illustrates an example of a thermallyconductive interface assembly that includes mechanical linkage. In FIG.6, the diagram 600 illustrates the thermally conductive interfaceassembly 102 movable between the first state 180 and the second state190 by a cam and a camshaft. The camshaft includes shape memory alloymaterial and is configured to rotate the cam to bias the thermallyconductive interface assembly 102 towards the first state 180 or thesecond state 190.

The diagram 600 includes a first representation of the thermallyconductive interface assembly 102 in the first state 180 and a secondrepresentation of the thermally conductive interface assembly 102 in thesecond state 190. The thermally conductive interface assembly 102further includes one or more cams and one or more camshafts configuredto generate a force to bias the thermally conductive interface assembly102 towards the first state 180. In the implementation illustrated inFIG. 6, a first cam 662 corresponds to the first fastener 122 and asecond cam 664 corresponds to the second fastener 124. For example, thefirst cam 662 is aligned with the first fastener 122. The first cam 662and the second cam 664 exert forces on the first component 112 to movethe first component 112 towards the second component 114.

In FIG. 6, the diagram 600 also illustrates a top view 670 of thethermally conductive interface assembly 102. The top view 670 depicts afirst shape memory alloy camshaft 630 coupled to a first fixed end 682and to the first cam 662 and a second shape memory alloy camshaft 632coupled to a second fixed end 684 and to the second cam 664.

During operation, at the first time, the shape memory alloy camshafts630 and 632 (e.g., shape memory alloy components) of the thermallyconductive interface assembly 102 reaches the first temperatureresponsive to receiving (directly or indirectly) thermal energy from theSun. Responsive to reaching the first temperature, the shape memoryalloy components generate a force to rotate the cams 662 and 664 to afirst orientation. Rotation of the cams 662 and 664 to the firstorientation (e.g., a major axis of the cams 662 and 664 parallel tointerface surfaces, such as the interface surfaces 152 and 154 of FIG.1, of the first and second components 112 and 114) biases the thermallyconductive interface assembly 102 towards the first state 180. The forcegenerated by the shape memory alloy camshafts 630 and 632 overcomes aforce generated by the first and second fasteners 122 and 124 thatbiases the thermally conductive interface assembly 102 towards thesecond state 190.

At the second time, the shape memory alloy camshafts 630 and 632 of thethermally conductive interface assembly 102 reaches the secondtemperature responsive to receiving (directly or indirectly) relativelyless environmental loading. Responsive to reaching the secondtemperature, the shape memory alloy camshafts 630 and 632 generate aforce to rotate the cams 662 and 664 to a second orientation. Rotationof the cams 662 and 664 to the second orientation (e.g., a major axis ofthe cams 662 and 664 perpendicular to the interface surfaces) biases thethermally conductive interface assembly 102 towards the first state 180.Responsive to the shape memory alloy camshafts 630 and 632 ceasing togenerate the force to bias the thermally conductive interface assembly102 towards the first state 180, the force generated by the first andsecond fasteners 122 and 124 biases the thermally conductive interfaceassembly 102 towards the second state 190.

In other implementations, a shape memory alloy component reconfigures togenerate a force to bias the thermally conductive interface assembly 102towards the second state 190 (close the thermal interface and eliminatethe gap 160). In such implementations, the shape memory alloy componentreconfigures to a compressed state, a twisted state, or an untwistedstate. Additionally, the thermally conductive interface assembly 102includes other components, such a heating element, a controller, one ormore fastener connectors (e.g., heat spreaders), as described withreference to FIGS. 1-5.

Additionally or alternatively, one or more of the shape memory alloycamshafts 630 and 632 may be activated or controlled by a controller andheating element, as described with reference to FIGS. 4 and 5. In suchimplementations, the thermally conductive interface assembly 102 isconfigured such that rotation of the shape memory alloy camshafts 630and 632 biases the thermally conductive interface assembly 102 towardsthe first state 180 or the second state 190. In addition, the thermallyconductive interface assembly 102 may include one more spacers, such asspacers 264 and 364 as described with reference to FIGS. 2-5. Further,the thermally conductive interface assembly 102 may include the thermalinterface material 136 of FIGS. 1-5.

By using the cams and the shape memory alloy camshafts a mechanicaladvantage may be obtained which increases a force generated by shapememory alloy components used to bias the thermally conductive interfaceassembly 102. Additionally, as the cams have a fixed displacement, thecams and the shape memory alloy camshafts may allow for a more precisecontrol of the gap 160 and a more precise control of the conductive heattransfer characteristics of the thermally conductive interface assembly102 as compared to the implementations illustrated in FIGS. 2-5.

In addition to, or in the alternative to, using shape memory alloyfasteners, as described with reference to FIGS. 1-5, or using shapememory alloy camshafts, as described with reference to FIG. 6, athermally conductive interface assembly may include a shape memory alloycomponent positioned in the thermal interface (e.g., positioned betweenthe first component 112 and the second component 114). As describedfurther with reference to FIGS. 7 and 8, the shape memory alloycomponent is a frame which partially surrounds a thermal interfacematerial, such as the thermal interface material 136 of FIG. 1. Asillustrated in FIGS. 7 and 8, the shape memory alloy frame is configuredto expand responsive to an increase in temperature to open the thermalinterface of the thermally conductive interface assembly. The firstcomponent 112 and the second component 114 are in contact via the shapememory alloy frame and the thermal interface material in the open state.

FIGS. 7 and 8 illustrate exemplary implementations of a thermalinterface material, such as the thermal interface material 136 of FIG.1, that includes a shape memory alloy frame. FIG. 7 illustrates a“corrugated” shape memory alloy frame 736 and FIG. 8 illustrates a“dimpled” shape memory alloy frame 836. A shape memory alloy frame maybe made of a shape memory alloy or of a non-shape memory metal (oralloy) which includes shape memory alloy features or elements (e.g.,tubing, threads, caps, pins, posts, or notches). The exemplary thermalinterface materials of FIGS. 7 and 8 may include or correspond to thethermal interface material 136 of FIGS. 1-6.

Referring to FIG. 7, a diagram 700 illustrates a top view 772 and sideviews 774 and 776 of the thermal interface material 136 that includesthe corrugated shape memory alloy frame 736. For example, in someimplementations the corrugated shape memory alloy frame 736 is formed orworked into a corrugated shape (wavy, uneven, ribbed grooved, etc.). Asthe corrugated shape memory alloy frame 736 experience a temperaturechange (e.g., heated or cooled) the corrugated shape memory alloy frame736 changes shape and exterior surfaces (e.g., surfaces further from acenter of the corrugated shape memory alloy frame 736) move outwardsfrom the center of the corrugated shape memory alloy frame 736 to open athermal interface of the thermally conductive interface assembly.

Referring to the top view 772, the thermal interface material 136 issurrounded by the corrugated shape memory alloy frame 736. Referring toa first side view 774, representations of the corrugated shape memoryalloy frame 736 are illustrated when the thermally conductive interfaceassembly 102 is in the first state 180 and the second state 190. Thefirst state 180 corresponds to the corrugated shape memory alloy frame736 being at or above the first temperature 492 and the second state 190corresponds to the corrugated shape memory alloy frame 736 being at orbelow the second temperature 494.

Referring to a second side view 776, three-dimensional representationsof the corrugated shape memory alloy frame 736 are illustrated,including a first representation of a portion of the corrugated shapememory alloy frame 736 at the first temperature 492 and a secondrepresentation of the portion of the corrugated shape memory alloy frame736 at the second temperature 494. As illustrated in FIG. 7, the portionof the corrugated shape memory alloy frame 736 has the first size 272(e.g., a vertical dimension as illustrated in FIG. 7) at the firsttemperature 492 and has the second size 274 at the second temperature494. The first size 272 corresponds to the first state 180 of thethermally conductive interface assembly 102. As illustrated in FIG. 2,the first size 272 is smaller than the second size 274.

Referring to FIG. 8, a diagram 800 illustrates the “dimpled” thermalinterface material includes shape memory alloy or shape memory alloyfeatures. For example, in some implementations the dimpled thermalinterface includes a thermally conductive base (e.g., copper) with shapememory alloy material deposited on the thermally conductive base to formdots or dimples. As the dots or dimples experience a temperature change(e.g., heated or cooled), the dots or dimples change shape and expandoutwards from the thermally conductive base to open a thermal interfaceof a thermally conductive interface assembly 102. Additionally, thethermal interface materials may be coupled to or include a heatingelement to control the thermal interface as described with reference toFIGS. 4 and 5.

Referring to the top view 872, the thermal interface material 136 issurrounded by the dimpled shape memory alloy frame 836. Referring to afirst side view 874, representations of the dimpled shape memory alloyframe 836 are illustrated when the thermally conductive interfaceassembly 102 is in the first state 180 and the second state 190 isillustrated. The first state 180 corresponds to the dimpled shape memoryalloy frame 836 being at or above the first temperature 492 and thesecond state 190 corresponds to the dimpled shape memory alloy frame 836being at or below the second temperature 494.

Referring to a second side view 876, three-dimensional representationsof the dimpled shape memory alloy frame 836 are illustrated, including afirst representation of the dimpled shape memory alloy frame 836 at thefirst temperature 492 and a second representation of the dimpled shapememory alloy frame 836 at the second temperature 494. As illustrated inFIG. 8, the corrugated shape memory alloy frame 836 has larger “dimples”at the first temperature 492 than at the second temperature 494.

By using thermal interface materials that include a shape memory alloyframe or a frame with shape memory alloy features, an existing thermalinterface may be retrofit to include passive or active control over heatrejected (or absorbed) by the thermal interface. The thermal interfacematerial and shape memory alloy frame may provide a greater force and amore even force distribution on the thermal interface than shape memoryfasteners alone. As compared to a thermally conductive interfaceassembly which includes a thermal interface material only, a thermallyconductive interface assembly which includes a thermal interfacematerial and shape memory alloy frame may have a lower thermalconductivity.

Two or more of the foregoing implementations of FIGS. 1-8 may becombined. For example, a thermally conductive interface assembly mayutilize passive activation and active heating. To illustrate, a firstsubset of fasteners of a thermally conductive interface assembly may bepassively heated to bias the thermally conductive interface assemblytowards an open state and a second subset of fasteners may be activelyheated by a heating element(s) to bias the thermally conductiveinterface assembly towards the open state or towards a closed state. Asanother example, a thermally conductive interface assembly may includedifferent types of shape memory alloy components. To illustrate, athermally conductive interface assembly may include the shape memoryalloy washers of FIGS. 1 and 2 and the shape memory alloy screws ofFIGS. 4 and 5. As another illustration, a thermally conductive interfaceassembly may include a shape memory alloy frame as in FIGS. 7 and 8 anda shape memory fastener as in FIGS. 1-5 or a shape memory alloy camshaftas in FIG. 6. The shape memory alloy components may have differentprogrammed shapes for a given temperature (or range of temperature) thusallowing different size gaps to be formed at multiple temperatures(e.g., allowing more than two states).

FIG. 9 illustrates a method 900 of operating a thermally conductiveinterface assembly. The method 900 may be performed by the thermallyconductive interface assembly 102 of FIGS. 1-8, the fasteners 122-132 ofFIGS. 1-8, the spacers 264 and 364 of FIGS. 2-5, the controller 408 ofFIG. 4, or a combination thereof. The method 900 includes, at 902,moving, by a shape memory alloy component of a thermally conductiveinterface assembly, one or more components of the thermally conductiveinterface assembly from a first state to a second state (or vice-versa)responsive to a first temperature. In the first state, a first interfacesurface of the thermally conductive interface assembly is in contact(e.g., direct physical contact or thermal contact via a thermalinterface material) with a second interface surface of the thermallyconductive interface assembly, and in the second state, a gap is definedbetween the first interface surface and the second interface surface.The thermally conductive interface assembly has first conductive heattransfer characteristics in the first state and has second conductiveheat transfer characteristics in the second state.

The shape memory alloy component may include or correspond to one ormore fasteners of the fasteners 122-132 of FIGS. 1-8, the thermalinterface material 136 of FIGS. 1-5, 7 and 8, the shape memory alloycamshafts 630 and 632 of FIG. 6, the shape memory alloy frame 736 ofFIG. 7, the shape memory alloy frame 836 of FIG. 8, or a combinationthereof. The thermally conductive interface assembly may include orcorrespond to the thermally conductive interface assembly 102 of FIGS.1-8. The one or more components may include or correspond to the firstand second components 112 and 114 of FIGS. 1-8, the fasteners 122-132 ofFIGS. 1-8, the thermal interface material 136 of FIGS. 1-5, 7 and 8, theheat pipes 142 and 144 of FIGS. 1 and 2, the spacers 264 and 364 ofFIGS. 2-5, the cams 662 and 664 of FIG. 6, or a combination thereof. Thefirst state may include or correspond to the second state 190 of FIGS.1-8 and the second state may include or correspond the first state 180of FIGS. 1-8. The first interface surface and the second interfacesurface may include or correspond to the first interface surface 152,the second interface surface 154, a surface of the first component 112,a surface of the second component 114, a surface of the thermalinterface material 136, a surface of the spacer 264, a surface of theshape memory alloy frame 736 of FIG. 7, a surface of the shape memoryalloy frame 836 of FIG. 8, or a combination thereof.

The method 900 of FIG. 9 further includes, at 904, moving, by the shapememory alloy component, the one or more components of the thermallyconductive interface assembly from the second state to the first stateresponsive to a second temperature. The first temperature may include orcorrespond to the first temperature of FIGS. 1-8 and the secondtemperature may include or correspond the second temperature of FIGS.1-8. In some implementations, the first temperature is greater than thesecond temperature, and in other implementations, the first temperatureis less than the second temperature.

In some implementations, the thermally conductive interface assembly isincluded in a vehicle and is configured to selectively reject heat fromthe vehicle (and/or electronic devices thereof) via a radiator, such asthe radiator 106, as described with reference to FIG. 1. In a particularimplementation, the thermally conductive interface assembly is locatedin a close-out panel of a spacecraft.

In some implementations, the thermally conductive interface assemblyincludes a thermal interface material positioned between the firstcomponent and the second component, and wherein the first interfacesurface corresponds to a surface of the thermal interface material. Insome implementations, the second interface surface corresponds to asurface of the first component 112, a surface of the second component114, a surface of the spacer 264, or a surface of another thermalinterface material.

In some implementations, the thermally conductive interface assemblyincludes a thermal interface material positioned between the firstinterface surface and the second interface surface, and the firstinterface surface is in thermal contact with the second interfacesurface via the thermal interface material in the first state. Forexample, as described with reference to FIG. 1, the first interfacesurface 152 is in contact with the second interface surface 154 via thethermal interface material 136 and conductively transfers the heatgenerated by the electronic device 104 in the second state 190.

In some implementations, in the first state, the thermally conductiveinterface assembly is configured to conductively transfer the heatgenerated by the electronic device from the first interface surface tothe second interface surface. In the second state, the thermallyconductive interface assembly is configured to prevent conductive heattransfer between the first interface surface and the second interfacesurface. As described with reference to FIG. 1, in the second state 190,the first interface surface 152 is in contact with the second interfacesurface 154 via the thermal interface material 136 and conductivelytransfers the heat generated by the electronic device 104. In the firststate 180, the first interface surface 152 is not in contact with thesecond interface surface 154 via the thermal interface material 136 anddoes not conductively transfer the heat generated by the electronicdevice 104. In the first state, the first interface surface 152 isseparated from the second interface surface 154 by an insulator, such asthe gap 160. In other implementations, the first and second state havethe opposite effect.

The method 900 may further include receiving heat from an externalsource, where the received heat causes a temperature change from thefirst temperature to the second temperature or from the secondtemperature to the first temperature. For example, the thermallyconductive interface assembly may receive solar radiation from the Sunand the solar radiation may cause a temperature change between the firstand second temperatures, as described with reference to FIG. 1

In a particular implementation, responsive to receiving heat from theexternal source, the shape memory alloy component transitions from acompressed shape to an expanded shape. The transition from thecompressed shape to the expanded shape moves the one or more componentsof the thermally conductive interface assembly from the first state tothe second state or from the second state to the first state.Alternatively, the shape memory alloy component transitions from atwisted state to an untwisted state. The transition from the twistedshape to the untwisted shape moves the one or more components of thethermally conductive interface assembly from the first state to thesecond state or from the second state to the first state.

The method 900 may further include providing heat, from a heatingelement, to the shape memory alloy component to transition the shapememory alloy component from a compressed shape to an expanded shape,where the heat causes a temperature change from the first temperature tothe second temperature or from the second temperature to the firsttemperature. For example, the heating elements 482 and 484 generate andprovide heat to the shape memory alloy components (e.g., the fasteners130 and 132), as described with reference to FIGS. 4 and 5. In otherimplementations, the heat provided by the heating element transitionsthe shape memory alloy component from the expanded or untwisted shape tothe compressed or twisted shape.

Referring to FIG. 10, a block diagram of an illustrative embodiment of aspacecraft 1000 (e.g., a manned or unmanned spacecraft). As shown inFIG. 10, the spacecraft 1000 (e.g., a spaceship, a satellite, or a spacestation) includes a frame 1018, an interior 1022, and a plurality ofsystems 1020. The systems 1020 may include one or more of a propulsionsystem 1024, an electrical system 1026, a hydraulic system 1030, anenvironmental system 1028, and a heat rejection system 1002.Alternatively, the heat rejection system 1002 may be part of theenvironmental system. Any number of other systems may be included in thespacecraft 1000.

The heat rejection system 1002 includes the thermally conductiveinterface assembly 102 of FIGS. 1-8 and a shape memory alloy component1032. The shape memory alloy component 1032 may include or correspond toone or more fasteners of the fasteners 122-132 of FIGS. 1-8, the thermalinterface material 136 of FIGS. 1-5, 7 and 8, the spacers 264 and 364 ofFIGS. 2-5, the shape memory alloy camshafts 630 and 632 of FIG. 6, theshape memory alloy frame 736 of FIG. 7, the shape memory alloy frame 836of FIG. 8, or a combination thereof. In the particular implementationillustrated in FIG. 10, the heat rejection system 1002 include thecontroller 408 and the first heating element 482. The thermallyconductive interface assembly 102 may be included in or coupled to anexterior surface of the spacecraft 1000. For example, the thermallyconductive interface assembly 102 may be include in a close-out panel ofthe spacecraft 1000. The heat rejection system 1002 is configured toreject heat from the spacecraft 1000 (or electronics thereof) asdescribed above with reference to FIGS. 1-9. For example, the controller408 may be configured to execute computer-executable instructions (e.g.,a program of one or more instructions) stored in a memory. Theinstructions, when executed, cause the controller 408 to perform one ormore operations of the method 900. For example, the controller 408 maysend control signals to the first heating element 482 to activate thefirst heating element 482 to open the thermal interface and todeactivate the first heating element 482 to close the thermal interface,as described with reference to FIGS. 4 and 5. Alternatively, the heatrejection system 1002 is passive and the shape memory alloy component1032 opens and closes the thermal interface dependent on externalloading (and independent of a controller 408).

The illustrations of the examples described herein are intended toprovide a general understanding of the structure of the variousimplementations. The illustrations are not intended to serve as acomplete description of all of the elements and features of apparatusand systems that utilize the structures or methods described herein.Many other implementations may be apparent to those of skill in the artupon reviewing the disclosure. Other implementations may be utilized andderived from the disclosure, such that structural and logicalsubstitutions and changes may be made without departing from the scopeof the disclosure. For example, method operations may be performed in adifferent order than shown in the figures or one or more methodoperations may be omitted. Accordingly, the disclosure and the figuresare to be regarded as illustrative rather than restrictive.

Moreover, although specific examples have been illustrated and describedherein, it should be appreciated that any subsequent arrangementdesigned to achieve the same or similar results may be substituted forthe specific implementations shown. This disclosure is intended to coverany and all subsequent adaptations or variations of variousimplementations. Combinations of the above implementations, and otherimplementations not specifically described herein, will be apparent tothose of skill in the art upon reviewing the description.

The Abstract of the Disclosure is submitted with the understanding thatit will not be used to interpret or limit the scope or meaning of theclaims. In addition, in the foregoing Detailed Description, variousfeatures may be grouped together or described in a single implementationfor the purpose of streamlining the disclosure. Examples described aboveillustrate but do not limit the disclosure. It should also be understoodthat numerous modifications and variations are possible in accordancewith the principles of the present disclosure. As the following claimsreflect, the claimed subject matter may be directed to less than all ofthe features of any of the disclosed examples. Accordingly, the scope ofthe disclosure is defined by the following claims and their equivalents.

1. An apparatus comprising: a thermally conductive interface assemblyincluding a first component associated with a first interface surfaceand a second component associated with a second interface surface; and ashape memory alloy component coupled to the thermally conductiveinterface assembly and configured to move at least the first componentof the thermally conductive interface assembly between a first state anda second state based on a temperature of the shape memory alloycomponent, wherein, in the first state, the first interface surface isin contact with the second interface surface, and in the second state, agap is defined between the first interface surface and the secondinterface surface.
 2. The apparatus of claim 1, wherein the shape memoryalloy component has an expanded shape responsive to a first temperatureand has a compressed shape responsive to a second temperature, andwherein the first temperature is greater than the second temperature. 3.The apparatus of claim 2, wherein a transition of the shape memory alloycomponent from the compressed shape to the expanded shape corresponds toa transition from the second state to the first state, and wherein oneof the first interface surface or the second interface surface iscoupled to a heat source and the other of the first interface surface orthe second interface surface is coupled to a heat sink.
 4. The apparatusof claim 2, wherein a transition of the shape memory alloy componentfrom the compressed shape to the expanded shape corresponds to atransition from the first state to the second state.
 5. The apparatus ofclaim 1, wherein the shape memory alloy component comprises a washer, anut, a spring, a bolt, or a gasket, and wherein the shape memory alloycomponent is further configured to move the second component, one ormore additional components of the thermally conductive interfaceassembly, or a combination thereof.
 6. The apparatus of claim 1, furthercomprising a heating element coupled to the shape memory alloy componentand configured to provide heat to the shape memory alloy component,wherein the thermally conductive interface assembly is configured totransfer heat from a heat source, and wherein the heating element isdistinct from the heat source.
 7. The apparatus of claim 1, furthercomprising a first heat pipe coupled to the first interface surface anda second heat pipe coupled to the second interface surface, wherein thefirst heat pipe and the second heat pipe are configured to exchange heatby conduction when the thermally conductive interface assembly is in thefirst state.
 8. The apparatus of claim 1, further comprising: a fastenercoupled to the thermally conductive interface assembly and configured toexert a force to bias the thermally conductive interface assemblytowards the first state; and one or more Belleville washers coupled tothe fastener and configured to exert a force to bias the thermallyconductive interface assembly towards the first state.
 9. The apparatusof claim 1, further comprising one or more Belleville washers positionedin a thermal interface of the thermally conductive interface assemblyand configured to exert a force to bias the thermally conductiveinterface assembly towards the second state.
 10. The apparatus of claim1, further comprising a thermal interface material positioned betweenthe first component and the second component, and wherein the firstinterface surface corresponds to a surface of the thermal interfacematerial.
 11. The apparatus of claim 1, wherein the shape memory alloycomponent comprises a thermal interface material positioned between thefirst interface surface and the second interface surface.
 12. Theapparatus of claim 11, wherein the shape memory alloy componentcomprises a corrugated thermal interface material or a dimpled thermalinterface material.
 13. (canceled)
 14. The apparatus of claim 1, furthercomprising a cam coupled to the thermally conductive interface assembly,wherein the shape memory alloy component comprises a camshaft and isconfigured to rotate the cam to move the thermally conductive interfaceassembly between the first state and the second state.
 15. A methodcomprising: moving, by a shape memory alloy component of a thermallyconductive interface assembly, one or more components of the thermallyconductive interface assembly from a first state to a second stateresponsive to a first temperature, wherein, in the first state, a firstinterface surface of the thermally conductive interface assembly is inphysical contact with a second interface surface of the thermallyconductive interface assembly, and in the second state, a gap is definedbetween the first interface surface and the second interface surface,and moving, by the shape memory alloy component, the one or morecomponents of the thermally conductive interface assembly from thesecond state to the first state responsive to a second temperature. 16.The method of claim 15, further comprising receiving heat from anexternal source, wherein the received heat causes a temperature changefrom the first temperature to the second temperature or from the secondtemperature to the first temperature.
 17. The method of claim 15,further comprising providing heat, from a heating element, to the shapememory alloy component to transition the shape memory alloy componentfrom a compressed shape to an expanded shape, wherein the heat causes atemperature change from the first temperature to the second temperatureor from the second temperature to the first temperature.
 18. Aspacecraft comprising: an electronic device; one or more internal heatpipes coupled to the electronic device; a thermally conductive interfaceassembly coupled to the one or more internal heat pipes, the thermallyconductive interface assembly including a first component associatedwith a first interface surface and a second component associated with asecond interface surface; and a shape memory alloy component coupled tothe thermally conductive interface assembly and configured to move atleast the first component of the thermally conductive interface assemblybetween a first state and a second state based on a temperature of theshape memory alloy component, wherein, in the first state, the firstinterface surface is in physical contact with the second interfacesurface, and in the second state, a gap is defined between the firstinterface surface and the second interface surface.
 19. The spacecraftof claim 18, wherein the thermally conductive interface assembly islocated in a close-out panel of the spacecraft, and wherein, in thefirst state, the one or more internal heat pipes are configured totransfer heat generated by the electronic device to the first interfacesurface and the thermally conductive interface assembly is configured toconductively transfer the heat generated by the electronic device fromthe first interface surface to the second interface surface.
 20. Thespacecraft of claim 18, wherein, in the second state, the thermallyconductive interface assembly is configured to prevent conductive heattransfer between the first interface surface and the second interfacesurface.
 21. The apparatus of claim 1, wherein the thermally conductiveinterface assembly is configured to conductively transfer heat betweenthe first interface surface and the second interface surface in thefirst state, wherein the thermally conductive interface assembly hasfirst conductive heat transfer characteristics in the first state andhas second conductive heat transfer characteristics in the second state,and wherein the first conductive heat transfer characteristics aregreater than the second conductive heat transfer characteristics.